1. Field of the Invention
The present invention relates to a step-and-repeat machine for use in photoengraving work, and particularly relates to a method of printing through a contact exposure in a step-and-repeat machine in which an original film and a photo-sensitive material are made to be in contact with each other by a vacuum.
2. Description of the Prior Art
A step-and-repeat machine is an apparatus for photocomposing a picture of an original film onto a photosensitive material such as a presensitized plate or the like. The photocomposing in the step-and-repeat machine is carried out through such a process that an original holder having a light-transmissible plate such as a glass plate for suction-holding an original film on the lower surface thereofis moved to one desired position or more on a photosensitive material mounted on a photosensitive material holder, the original film and the photosensitive material are made to abut each other at the above-mentioned desired position at the same time air is evacuated out of a space enclosed by the light-transmissible plate of the original holder. The photosensitive material (or the photosensitive material holder) and airtight packing are provided along the periphery of the light-transmissible plate at its circumference so that the original film and the photosensitive material are made to come into close contact with each other by a vacuum. Then, a light source provided behind the original film is turned on so that the picture of the original film is printed on the photosensitive material.
In the step-and-repeat machine described above, however, a phenomenon of vagueness often occurs in a printed picture particularly in the case where printing is carried out at a position where the light-transmissible plate for vacuum-holding the original film on the original holder is in the state of mounting over an end of the photosensitive material. This is because the photosensitive material, such as a presensitized plate or the like, is made by applying a photosensitizer onto a surface of an aluminum plate, and therefore the light-transmissible plate may be curved owing to the thickness of the aluminum plate or the like when the original film is placed into vacuum-contact with the photosensitive material so that the original film being vacuum-held by the light-transmissible plate is made to curve similarly to the curve of the light-transmissible plate to thereby cause a phenomenon that the original film and the photosensitive material do not completely come into close contact with each other over all the area of the original film. Further, in the case where a lamination of a plurality of films is used as the original film, such a phenomenon as described above often occurs owing to the thickness of the lamination of films.
In order to solve the disadvantages described above, Japanese Patent Unexamined Publication No. 56-38036 discloses a step-and-repeat machine in which a surface of a photosensitive holder for holding a photosensitive material is made of a flexible material such as a flexible metal plate or the like and an air-flowing portion is provided for exposing the back surface of the flexible plate to the air, so that the flexible plate is made to curve along the photosensitive material when the original film is made into vacuum-contact with the photosensitive material.
In the step-and-repeat machine disclosed in the above Japanese Paten Unexamined Publication No. 56-38036, however, in the case where a relatively hard material such as a relatively hard metal plate is used as the flexible plate, the thickness of the photosensitive material cannot be completely accommodated by the flexible plate, so that a phenomenon of vagueness in print cannot be eliminated particularly in the vicinity of a step portion owing to the thickness of the photosensitive material or the like. Accordingly, it is considered that a soft material such as a plate of soft vinyl chloride or the like is used as the flexible plate. Even in that case, not only the vagueness phenomenon can not be completely eliminated, but there is a further problem that a mark of the end portion of the photosensitive material is left on the surface of the soft material in the vacuum contact so that the life of the soft material is made short.